A variety of technologies implement ceramic filters, including both monoblock filters and duplex filters. For instance, transmitters and receivers in radio equipment utilize the same antenna, and thus the transmission network controls both the transmission signal and the receiving signal. Ceramic filters, such as duplex ceramic filters including two individual band-pass filters, are typically employed in such radio equipment to reduce interference. One filter connects the receiving branch and has a center frequency and bandwidth corresponding to the receiving band. The other filter connects the transmission branch and has a center frequency and bandwidth corresponding to the transmission band. Conventional ceramic filters include a dielectric ceramic material for the main body upon which metallic materials are applied for producing conducting paths. These paths define the performance of the filter and are used for realization of pads or other isolated conducting areas that contact the printed circuit board or other interface material.
Air cavity duplex filters are often used in high power or macro-class base transceiver stations (BTS), which operate at higher power levels (i.e., on the order of Watts to many Watts of transmitted RF power). Such filters include multiple resonators which, when tuned properly, can operate in concert to achieve desired filter performance needs. The implementations inherent in air dielectric filters are such that sufficient separations between conductive elements can be achieved in order to prevent arcing between elements when the filters are operated at high power levels. However, air dielectric filters are large and heavy devices which make them prohibitive for use in applications that require small size and low weight. Thus, emerging ceramic filter technologies may be utilized to meet those needs in many applications. These ceramic filters have the characteristic that they are much smaller and weigh much less than conventional air dielectric filters. However, ceramic filters are limited to operation at peak and average power levels significantly lower than those offered by air dielectric filters. Moreover, recessed top pattern (RTP) filters are often limited by peak power handling due to the possibility of electrical arcs, which is strongly dependent on environmental factors such as humidity and air pressure.
Accordingly, since peak power handling of RTP filters is limited by environment conditions such as humidity and air pressure, there is a need to provide ceramic filters in a controlled local environment for higher power handling. There is a further need to ensure that such a controlled local environment for the ceramic filter does not change over time regardless of the conditions of the exterior environment.